Star couplers are optical devices used in the field of fiber optics for mixing together a plurality of light signals from different optical fibers and supplying all of those signals to a plurality of output optical fibers. Several different star couplers are known. In general, the couplers have a plurality of incoming channels, a plurality of outgoing channels, and a mixing zone that couples optical signals from any one of the incoming channels to all of the outgoing light conveying devices or optical transmission devices. The mixing zone may be optic fibers tapered and fused together, or a waveguide-like solid block of glass or other transparent material. Transparent mixing blocks are typically clad with a material having a refractive index lower than that of the core material of the mixing blocks. The core is the central region of an optical transmission material.
In some applications, it is advantageous to have either the input or the output of a star coupler terminate onto an optoelectronic device such as a photo diode or light emitting diode (LED). One approach is to break a fused fiber bundle in the middle of the taper of the fused portion so that light may be coupled to and from this region onto a single optoelectronic device.
Planar and mixing rod structures are employed to perform the function of a star coupler mixing region. Optical fibers abut one end of the mixing rod or planar region so that light passing through the mixing rod is optically introduced into the optical fibers. The following U.S. Patents disclose various implementations of a mixing rod in an optical coupler device. U.S. Pat. No. 4,995,692 to Diliello et al., U.S. Pat. No. 4,198,118 to Porter, U.S. Pat. No. 4,653,845 to Tremblay et al. and U.S. Pat. No. 5,019,301 to Coden et al.
In certain applications, it is desirable to mix light from several different active sources, wherein each source produces light with a frequency content centered in a narrow range of frequencies. The mixing of light from several different sources is necessary or desired particularly in the field of spectroscopy, wherein light reflected from a target is analyzed to determine the percentage of light that is reflected by the target. Such devices are commonly referred to as reflectance meters. A compact device that efficiently and accurately combines the light from multiple light sources and that supplies the light to multiple optical fibers is needed for highly accurate spectroscopy devices. Examples of such devices are blood oxygen measuring devices and blood glucose measuring devices used by many diabetics.